How much is a life worth?

We don't like putting a dollar figure on the value of a human life, especially ex ante, but when we're trying to evaluate the wisdom of regulation, it's an unavoidable inquiry, and federal agencies are currently revising their calculations.  It still makes me squirm though, as I think it should.  As I remind my Torts students, if we truly viewed human life as priceless beyond all measure, wouldn't we have prohibited car manufacturers from designing vehicles that go faster than 30 mph?